Breathing in greater depth than you ever cared to know

What you may know

Breathing is controlled by pH and the following reaction

Also, hemoglobin (Hb) is the oxygen transporting protein carried by red blood cells (RBCs).
Fun fact: RBCs eject their nucleus as part of their normal life cycle and become little more than sacks of Hb. :D

Onto what you likely don't know:

Hemoglobin

is made of four protein chains, two alpha and two beta chains. Each chain holds one heme, giving each Hb a total of four hemes.

What is a heme, you ask? A heme is a large, planar, geometric molecule that stabilizes one iron(II) atom. This is where oxygen binds to Hb.

Histidine is an amino acid that plays a HUGE role in the way Hb is able to bind oxygen. The histidine in Hb alpha or beta is associated with the iron(II) atom in a heme due to an ionic intermolecular force using the highlighted hydrogen projecting from HIS' sexy, sexy face.

When oxygen is not bound to the iron(II), the atom hangs below the plane of the heme. This is called the relaxed (R) form.

When oxygen binds to the iron(II) it pulls the atom up and into the plane of the heme. This tugs on the histidine and changes the shape of the entire chain (subunit). We call this the taut (T) form of a chain. If one chain (alpha or beta) is in the T conformation it also tugs on the adjacent chains, making it slightly easier for the next iron(II) to bind with another oxygen molecule.

Super cool, right? This is called cooperation. Go figure.

 

Haldane Effect

When the concentration of carbon dioxide in the blood is high (in venous blood) it is easier for the carbon dioxide to bind to its own binding site on the Hb subunit. When carbon dioxide binds to Hb it causes an opposing structural change that helps to release oxygen!

When the concentration of carbon dioxide is low, like in the lung capillaries, oxygen binds again and causes a structural change that releases carbon dioxide. Neat, right?

Wait! There is more!

 

At high altitudes

Hb must bind oxygen especially well because tehr eis less of it available. One of the ways that the bodies of people who are acclimated to the altitude ope with how "grabby" the Hb is with oxygen is to increase levels of a chemical called 2, 3 bisphosphoglycerate (2, 3-BPG). This is anotehr allosteric ligand, similar to the way carbon dioxide works. In venous blood, 2, 3-BPG will "muscle" into the very center of tan Hb protein, among the four subunits and release the oxygen! When it reaches the lungs it dissociates from the Hb and allows oxygen to bind again!

 

 

Fetal Hb

binds oxygen more tightly so that it can take oxygen from the mother's blood and transport it to the fetus.

 

Myoglobin

Is a singular subunit (one alpha, one beta) that is used to store, but not transport oxygen. It doesn't form sites for allosteric binding to release the oxygen. It is found most in muscle tissue!

 

Bringin' it together

When carbonic anhydrase (best dive around) catalyzes the reaction laid out at the beginning of this section, blood pH increases and stimulates chemoreceptors in the carotid and aortic blood vessels as well as receptors in the medulla oblongata. This stimulates the phrenic and thoracic nerves and contracts the diaphragm.

 

 

SUPER COOL! YEAH! :D